The Apolyton Civilization 3 Democracy Game. This combines two of my gaming loves – Civ3, and mmoe. The premise is that over one hundred people are democratically playing a game of Civilization 3, electing a cabinet, detailing a constitution, forming numerous political parties and even newspapers. It sounds a little far-fetched but at only 14 turns into the game the participants are having a busy time discussing what to do with their neighbours, France (consensus: destroy them with extreme prejudice) and whether founding a city in a jungle was such a bad idea.
It wouldn’t be possible to do this sort of thing with many games other than Civ3, due to its complexity and richness; likewise, any alternate reality game or mmoe must have a certain level of detail and complexity in order to allow a community to grow up around it to carry the game forward.